1. Field of the Invention
The invention relates in general to signal detection, and more particularly to a successive interference cancellation method and apparatus and a detection method and apparatus using successive interference cancellation.
2. Description of the Related Art
In a code division multiple access (CDMA) communication system, signals of multiple users are overlapped in a time domain and in a frequency domain. As the signals of the users are correlated at a certain level, multiple access interference (MAI) is caused. The MAI includes priori information, such as known user channel codes and channel estimations, utilized for signal separation. A method that considers the separation of all user signals by fully employing the priori information in the MAI as a unified process is referred to as a multiple user detection-joint detection (MUD-JD). Among various MUD-JD techniques, successive interference cancellation (SIC) is prevalent.
It is discovered by the Applicant in long-term researches that, due to high-speed movements of a terminal, a greater Doppler shift is generated at user signals of a neighbor cell channel. In current successive interference cancellation methods, influences of a frequency shift of a neighbor cell channel upon a successive interference cancellation determination and reconstruction process are not considered. Referring to FIG. 1, assuming that an error block rate is 0.01, detection performance of successive interference cancellation without considering the frequency shift of a neighbor cell channel is −27.3 dB, detection performance of successive interference cancellation with a 100 Hz frequency shift in a neighbor cell channel is −23.2 dB, and detection performance of successive interference cancellation with a 200 Hz frequency in a neighbor cell channel is −19.5 dB. Thus, compared to successive interference cancellation perform without considering the frequency shift of a neighbor cell channel, successive interference cancellation performed with a 100 Hz frequency shift in a neighbor cell channel suffers from a 4.1 dB detection performance loss, and successive interference cancellation performed with a 200 Hz frequency shift in a neighbor cell channel suffers from a 7.8 dB detection performance loss. As seen from the above, the frequency shift of a neighbor cell channel causes errors in determined and reconstructed signals after the successive interference cancellation, leading to degradation in accuracy of the successive interference cancellation as well as in system detection performance.